The French patent application No. 2 307 596 describes a foundry molding box in which a device for feeding and recovering the granular material is provided for. Such device consists of a volume approximately in the shape of a truncated cone whose smaller base is equipped with a trap door through which the filling tube can be inserted; such trap door is airtight and remains closed for the whole duration of the box operation. Upon completion of the molding, the vacuum is broken as the box is turned over and the door trap opens, thus letting the material fall out by gravity.
Such a device and such a method allow only for slow molding rates as numerous handling operations prove necessary. Furthermore, casting is carried out with the mold maintained in the two molding boxes, which ties up two costly boxes to produce one single mold. In addition, it is necessary to carry out twice the forming operation in order to obtain the upper and lower parts of the mold in order for this dual operation to result in a complete mold.
A device and method permitting to eliminate in part those disadvantages as described in the French patent application No. 87 10514 are already well-known. The device in question differs from similar ones in the sense that it is made of at least two pattern-plates placed in the corresponding housings of a support, and of at least one sealing plate and one grid with two faces. The pattern-plate supporting components and the sealing plates are hinged with one another. The polymer film is a single film which corresponds to the surface area of the sealing plates and pattern-plates.
The method consists mainly of preparing the pattern-plates in the support, laying on top of such plates a polymer coating through heat-forming and suction through the plates, installing the pattern-plates around a grid with no more than three faces, ensuring the tightness between the polymer film and the grid by shrinking the film between the grid and the plates, or by applying the film onto the grid through pressure-sealing, filling with granular material, welding together the ends of said sheath over the upper grid and bringing together the cakes thus obtained to make prints.
This device and this method enable to achieve movements with reduced handling operations. In addition, only the grid and polymer sheath are used at the casting station and the grid is much simpler than the boxes previously used, thus resulting in a rather low investment. Furthermore, one single operation is sufficient to obtain both parts of a mold, which improves the output by close to 50%. The process is semi-continuous, but the casting can be continuous by juxtaposing the cakes. The number of parts required is small, just like the volume of granular material used.
However, the use of a two-face grid does not lend itself very well to roller handling and the length of stroke and size of the masses to be moved limits its performance. The device and method under the invention aim at correcting these disadvantages by proposing a pattern-plate support with sliding and pivoting caissons connected to a vacuum source, capable of lying flat against the grid after interposition of a polymer film, with the upper parts of said film being applied against the top of the grid under the action of air pressure and depression.